Annular seals in pumps such as liquid fuel pumps necessarily operate in a changing and severe environment. The operating parameters include small running clearances, wide temperature ranges, high surface velocities, extreme hydraulic axial loads due to high pressure differentials and the presence of contaminants such as sand and iron oxide in the fuel which degrade the integrity of the seal faces by erosion. In order for a seal to survive such a rugged environment, the seal material must have characteristics of high hardness, low coefficient of friction, and high thermal conductivity. Most materials that have been determined to satisfy these requirements have an inherent high modulus of elasticity and a low thermal expansion. In order to maintain a constant running clearance between the annular seal and rotating centrifugal impeller of the pump throughout the entire operating range of the pump, the difference in thermal expansion of the seal and impeller must be compensated for.
Examples of prior art which deal with the problem of providing a seal for the gap between two parts which may rotate relative to one another are shown in U.S. Pat. Nos. 2,851,289; 3,460,843; 4,575,306; 4,579,352; and 4,653,980.